Akin began running a TV ad claiming "the stimulus made McCaskill rich." In an interview with The Associated Press, Akin said the 2009 stimulus law funded a federal program for low-income housing that directed about $1 million to corporations affiliated with McCaskill's husband. He stopped short of accusing McCaskill of a conflict of interest, but he suggested she knew of the funding — pointing to McCaskill's own statements that she reviewed the bill "line by line."

"She went through it line by line, and a million dollars went to her family business — I think it was that simple," Akin said.

McCaskill denounced the assertions as "completely wrong" and referred further questions to her campaign staff.

McCaskill's husband, Joseph Shepard, had only a small ownership stake and received just several thousand dollars from the companies at issue, her campaign said. The stimulus bill did not specifically direct any money to Shepard's companies, but rather allotted $2 billion to a program in the Department of Housing and Urban Development, which distributed it among more than 6,000 contractors who ran subsidized housing units.

Akin, a congressman from suburban St. Louis, voted against the stimulus act and McCaskill voted for it, an action that each has defended in the context of a broader debate about the nation's economy. But Akin's assertion that McCaskill personally benefited from the law marked his most aggressive move yet in the race. Akin has generally been on the defensive, largely because of remarks he made last month about women having a biological means of averting pregnancy in "legitimate rape."

Top national Republicans pulled their financing and called upon Akin to drop out of the race after the rape remark. Akin apologized but refused to quit, and has slowly been rebuilding GOP support after a drop-out deadline passed last week.

The attack on McCaskill's family finances may be evidence that GOP support is coalescing around Akin. The supporting documents for the ad originally were intended for one of Akin's rivals in the GOP Senate primary. And the substance of the accusations originally was posted online in April by American Crossroads, a group affiliated with GOP strategist Karl Rove that has pulled its ads from Missouri.

McCaskill married Shepard in 2002 and the couple keeps separate finances, Legacki said. Yet McCaskill's opponents have long made an issue of Shepard's wealth and his complicated business dealings.

In the 2004 gubernatorial primary, Democratic Gov. Bob Holden aired an ad accusing Shepard of running dangerous nursing homes that helped finance McCaskill's campaign. In the 2006 Senate race, Republican Sen. Jim Talent ran an ad accusing Shepard and McCaskill of using an insurance company based in the Bahamas as a tax shelter, which they denied.

Akin's ad focuses on about $1 million of stimulus-funded payments made by HUD to subsidized housing developments in Illinois, Kansas, Missouri and New Mexico. The payments went to companies in which Shepard had assets, according to McCaskill's personal financial disclosure statements filed with the federal government.

But Akin's ad may overstate how much of that money went directly to Shepard. The financial disclosure statements show Shepard received between $2,800 and $9,600 from the companies at issue in those years. McCaskill's campaign said Shepard's ownership stake in the developments ranged from 5 percent downward to less than a single percentage point.

The Department of Housing and Urban Development determined how to divvy up the money in the stimulus act. The agency said the money was intended to ensure timely payments to businesses already under contract to provide low-income housing. It noted that payments in prior years had been delayed by budget shortfalls and congressional standoffs. The stimulus bill ensured the housing contractors got what they were owed, the agency said.

As Akin launched his new ad, McCaskill's campaign countered by criticizing Akin for missing most of the House votes taken since July.

"In the real world, he'd have been fired from a job, and if he was in the military, he'd be considered a deserter," said Bob Murphy, an Army veteran from St. Charles who participated in a conference call organized by McCaskill's campaign.

Akin said he chose to campaign in Missouri instead of casting certain votes in Congress because he said the Democratic-led Senate has refused to act on many of the priorities passed by the Republican-led House.

"I felt like it was probably better to try to do what I could to fix the problem, which is to change the Senate," Akin said.